| Organic electroluminescence (EL) is the electrically driven emission of light from noncrystalline organic materials, which was first observed and extensively studied in the 1960s. In 1987, a team in Kodak introduced a double layers organic light-emitting device (OLED), which combined modern thin film deposition techniques with suitable materials and structure to give moderately low bias voltages and attractive luminance efficiency. Shortly afterwards, in 1990 the Cambridge group of Friend announced a conducting polymer-based LED. Since then, there have been increasing interests and research activities in this new field, and enormous progress has been made in the improvements of color gamut, luminance efficiency and device reliability. The growing interest is largely motivated by the promise of the use of this technology in flat panel displays. As a consequence, various OLED displays have been demonstrated. The design of EL materials for used in OLEDs is critical to device performance. Intense research in both academia and industry over the last years has yielded OLEDs with remarkable color fidelity, device efficiencies and operational stability.Significant progress has been made recently in developing phosphorescent emitters via triplet-triplet energy transfer, and high-efficiency OLEDs in various colors have been demonstrated. Light extraction is determined by the device structure and the refractive indices of the composed layers. Current research activity is directed toward various surface modifications that can increase extraction efficiency, while the problem of light-trapping remains unsolved in terms of its application to displays.The most critical performance characteristic for OLEDs is the deviceoperational lifetime. Continuous operation of OLEDs generally leads to a steady loss of efficiency and a gradual rise in bias voltages. Although OLEDs have achieved long operational stability, the material issues underlying the EL degradation are not fully understood. The promise of low-power consumption and excellent emissive quality with a wide viewing angle is unique among display technologies. At the moment, passive monochrome and multicolor displays are commercially available, and active-matrix full-color displays have been demonstrated. Some important issues relating to display fabrication and the status of display development will also be described.Charge injection and transport are the limiting factors in determining operating voltage and luminance efficiency. The efficiency of an OLED is determined by charge balance, radiative decay of metal-organic interactions. In OLEDs, both operating voltage and luminance efficiency of the devices strongly depend on effective charge injection from the electrodes to the organic medium and charge transport in the organic materials. In general, to achieve the lowest possible voltage it is necessary to have Ohmic interfaces between the organic layers and the charge-injecting contacts and to maximize the drift mobility of both types of carriers. Furthermore, charge injection and charge transport also play an important role in optimizing the device efficiency of an OLED. An unbalanced injection results in an excess of one carrier type that does not contribute to light emission, and it can also result in an enhanced non-radiative recombination because of interactions of excitons with the charge carriers. To date, hole transport materials (HL) are greatly more than electron transport materials (EL), so we must energetically develop EL. One of the most widely used electron-transport and hole blocking materials is 2-(4-biphenyl)-5-(4-t-butylphenyl)-l, 3, 4-oxadiazole(PBD), it is due to oxadiazole cycle containing nitrogen atom which attracts electron, as a result, oxadiazole derivatives have a lower LUMO energy lever.In this paper, we synthesized 5 kinds of 5-aryl-2-mercapto-l, 3, 4-Oxadiazoie (AMO), 3 kinds of 2-aryl-5-aryl-l, 3, 4-oxadiazole(AAO), 7 kinds of 3-aryl-6-aryl-l, 2, 4-triazolo[3, 4~b]-1, 3, 4-thiadiazole(AATT) and 4 kinds of 2-aryl-3... |
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